Finite-Element Analysis of Interlaminar Shear Stress Due to Local Impact

Abstract

Interlaminar delamination may occur as a result of a nonperforating low-velocity impact of a foreign object against a continuous-fiber composite laminate. Experimental evidence shows that for a crossplied laminate consisting of three lamina and subjected to a central localized impact, one delamination region will extend farther from the impact point than the second region. To establish a quantitative value for the interlaminar shear stress of a crossplied fibrous composite plate subjected to a central impact, a finite-element computer program has been utilized. Specifically, a three-dimensional dynamic-elastic-orthotropic-material finite-element program has been used in which the interlaminar shear stress can be calculated directly. This program was used to evaluate the interlaminar shear stresses for a [05/905/05] glass/epoxy plate with built-in edges, and subjected to a load simulating a central localized impact of 45.7 m/s by a cylindrical steel projectile. Results of the calculations show a region of large shear stress (exceeding the estimated shear strength of the matrix material) extending from the impact point toward the boundary in the 0-deg direction while a region of large shear stress in the transverse 90-deg direction was found to be much smaller. Also, only minor differences in calculated shear stresses were evident in the interlaminar plane immediately below the impact point when compared with the interlaminar plane farthest from the impact point. The high-shear-stress regions agreed qualitatively with the areas observed in experiments.